1. Field of the Invention
The present invention relates generally to ultra fine and nanosized powders, components and coatings and particularly to ultra fine and nanosized powders, components and coatings of refractory metals, for example tungsten, tantalum, molybdenum, rhenium, iridium, niobium, zirconium, and hafnium, and to related ceramics, for example tungsten carbide, molybdenum carbide, and other ferrous (Iron) and non-ferrous materials like aluminum, copper, silicon, vanadium, titanium and nickel and their oxides, nitrides and borides, and to a method of fabricating same.
2. Description of the Related Art
There is great interest in the formation and use of refractory metals, for example, tungsten, tantalum, molybdenum, rhenium, and hafnium, and related ceramics. Typical refractory metals and related ceramic materials are often commercially available in powders with particle sizes from 40-80 micron. These elements and compounds have the following corresponding symbols:
TungstenWRheniumReMolybdenumMoHafniumHfTantalumTaIridiumIrNiobiumNbZirconiumZrMolybdenum CarbideMoCTungsten CarbideWC, W2C
These materials are resistant to heat and have high melting temperatures. Some of these elements also have other desirable properties, including chemical stability, hardness, and ductility. These characteristics make these materials particularly useful in high temperature applications such as propulsion, X-ray targets and furnace systems. These materials, however, also have drawbacks. For example, the commercially available powders, with their relatively large grain size, often suffer from poor ductility and decohesion of the large grains at elevated temperatures, and may be brittle. Moreover, conventional tungsten materials, for example, often have to be forged to get adequate heat resistant properties. Forging tungsten into complex shapes is difficult, time consuming (often taking months), and has limited its application, particularly in propulsion applications. Forged tungsten can also suffer from unacceptably low fatigue values and crack resistance. Additionally, traditional fabrication techniques require that each part be machined from a large billet, which produces higher waste and significantly increases fabrication time. Also, the use of expensive machining processes such as electrical discharge machining (EDM) and diamond grinding are often required since coarse grained refractory materials are brittle at room temperature and very difficult to machine.
By reducing the grain size through innovative processing, the properties of the metals, including refractory metals, ceramic, and related materials can be greatly improved. The designation of nano materials (i.e., nanostructured or nanocrystalline) is usually used to describe materials with a particle diameter less than or equal to 100 nanometers. For the applications herein, materials and powders described as “ultra fine” generally contain a large portion nano sized materials (i.e., less than 100 nm), but may also contain some larger sized particles, for example up to 300 nm. Mechanical properties of ultra fine and nanostructured materials show remarkable improvement or deviation from the properties exhibited by coarser grained material. These unique properties are attributed to the significant increase in grain boundary area due to the small grain size. In terms of the mechanical properties, ultra fine and nanostructured metals have shown increases in hardness values, ultimate strength, and yield strengths. Also, ultra fine and nanostructured metals have shown a clear increase in hardness with decreasing grain size, following the well known Hall-Petch equation. Ultra fine and nanostructured ceramics have exhibited superplastic properties at low temperatures. This is significant because coarse-grained tungsten is brittle like ceramics materials at low temperatures. Also, further deviations from trends observed in conventional materials are observed in creep of ultra fine and nanostructured metals due to the decreased grain size. The reduced grain size also provides a significant increase in fatigue and crack resistance. Thus, there is growing demand for ultra fine and nanostructured materials. Development of these ultra fine and nanosized materials will allow the production of robust components with unique properties with reduced size and weight.
Current manufacturing processes for ultra fine and nanostructured powders of refractory metals and related ceramics are limited by expense, feedstock availability, low production volumes and products with inconsistent particle size, distribution, shape and impurities.
3. Summary of the Invention
Applicant has discovered that particular methods of thermal plasma processing of certain materials produce high purity metal, including refractory metal, ceramic, and other similar materials in the form of an ultra fine powder and nanopowder and components. Plasma processing offers a wide range of new and sophisticated operations for the production of these advanced materials. Plasma processing combines various processes, such as heating, melting, quenching, and consolidation of fine particles (metallic or ceramic) in a simplified process.
Advantages of thermal plasma processing include, high purity resulting materials, high enthalpy to enhance the reaction kinetics by several orders of magnitude, steep temperature gradient that enables rapid quenching and generation of fine particle size powder, components and coating, little or no hazardous waste by-products, and low cost with bulk production capacity (over 10 kg/hr for basic powder operation). The methods described herein also allow processing of inexpensive precursors (or feedstock). Moreover, for the direct deposit fabrication methods discussed herein, fabrication times for complex parts are reduced from months to days.
The products and methods discussed herein are applicable to many of the refractory metals, for example tungsten, tantalum, molybdenum, rhenium, iridium, niobium, zirconium, and hafnium, and to related ceramics, for example tungsten carbide, molybdenum carbide, and other ferrous (Iron) and non-ferrous materials like aluminum, copper, titanium, silicon, vanadium, and nickel and their oxides, nitrides and borides. For ease of reference, the detailed description will focus primarily on one refractory metal, tungsten, as a representative material, but such description is not a limitation on the applicability of the invention to other materials, including those identified above. One major benefit of nanocrystalline and ultra fine bulk tungsten is enhanced dynamic deformation behavior, specifically shear localization. Ultra fine and nanostructured tungsten, when used as a kinetic energy device, offers the opportunity for performance that exceeds depleted uranium.
Applications of ultra fine and nano materials disclosed herein include, but are not limited to, superior weapon systems for armor and anti-armor applications, high kinetic energy penetrators in tank ammunitions, armor plating, and scatter grenades, counterweights in tanks, non-eroding rocket nozzles and jet vanes and welding electrodes, crucibles, nuclear power, propulsion components (high-powered electrical, beamed energy, and nuclear), cartridges, X-ray targets and heat pipes.
These and other embodiments of the present invention will also become readily apparent to those skilled in the art from the following detailed description of the embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.
In one embodiment a method of producing ultra fine powders, including nanopowders, through thermal plasma processing is provided comprising the steps of (a) vaporizing a precursor having at least one metal in a plasma jet plume; and (b) inducing rapid solidification of said metal vapor in a substantially inert environment to obtain the ultra fine powder. This embodiment may further include the step of inducing chemical reaction of the metal vapor.
In another embodiment, an ultra fine powder with particle size between 25-300 nm is produced by vaporizing a precursor having at least one metal in a plasma jet plume of at least 3000 K and rapidly inducing solidification of said vapor.
In another embodiment, a process for depositing ultra fine particles onto a substrate through thermal plasma processing comprising the steps of (a) vaporizing a precursor having at least one metal in a plasma jet plume having a temperature of more than about 3000 K to obtain vaporized metal particles, (b) inducing solidification of the vaporized metal; and (c) depositing the metal directly onto the substrate.
In another embodiment, a nanopowder is provided comprising particles having a size of approximately about 50-300 nm, produced by vaporizing a precursor compound in a plasma jet plume having a temperature of at least about 3000 K to separate said precursor compound into two or more vaporized constituent elements and inducing rapid solidification of at least one of said vaporized constituent elements in an inert environment.
In another embodiment, a nanostructured material coating is formed by vaporizing a precursor having at least one metal in a plasma jet plume of at least about 3000 K, inducing solidification of the vaporized metal, and depositing the metal onto the component to be coated.